diff --git a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/CustomFlashEvent.kt b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/CustomFlashEvent.kt
new file mode 100644
index 0000000..6d9abcd
--- /dev/null
+++ b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/CustomFlashEvent.kt
@@ -0,0 +1,49 @@
+package cn.rdlevel.rdkt.core.events
+
+
+import cn.rdlevel.rdkt.core.data.*
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+/**
+ * Emits a flash with custom settings.
+ * @property startColor The start color of the flash.
+ * @property startOpacity The start opacity of the flash.
+ * @property endColor The end color of the flash.
+ * @property endOpacity The end opacity of the flash.
+ * @property background Whether the flash should be a background flash or a foreground flash.
+ */
+@Serializable
+@SerialName("CustomFlash")
+public data class CustomFlashEvent(
+    var startColor: Color? = WHITE,
+    var startOpacity: Int? = 100,
+    var endColor: Color? = WHITE,
+    var endOpacity: Int? = 0,
+    var background: Boolean = false,
+    override var duration: Double = 2.0,
+    override var ease: Easing = Easing.LINEAR,
+    override var rooms: RoomsOrTopLayer = roomsOf(ROOM1),
+) : ActionEvent(), MutableRoomsOrTopLayerSpecificEvent, DurationEaseSpecificEvent {
+    /**
+     * The start color and opacity converted into [ColorWithAlpha].
+     * It will be null if either the color or the opacity is null.
+     */
+    var start: ColorWithAlpha?
+        get() = startOpacity?.let { startColor?.withAlpha((it * 255 / 100).coerceIn(0, 255)) }
+        set(value) {
+            startColor = value
+            startOpacity = value?.alpha?.let { it * 100 / 255 }
+        }
+
+    /**
+     * The end color and opacity converted into [ColorWithAlpha].
+     * It will be null if either the color or the opacity is null.
+     */
+    var end: ColorWithAlpha?
+        get() = endOpacity?.let { endColor?.withAlpha((it * 255 / 100).coerceIn(0, 255)) }
+        set(value) {
+            endColor = value
+            endOpacity = value?.alpha?.let { it * 100 / 255 }
+        }
+}
\ No newline at end of file
diff --git a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/EventProperties.kt b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/EventProperties.kt
index 5be580a..fbcb1c8 100644
--- a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/EventProperties.kt
+++ b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/EventProperties.kt
@@ -43,6 +43,21 @@ public interface DurationSpecificEvent : Event {
     public var duration: Double
 }
 
+/**
+ * An [Event] that has an easing, meaning it can have a smooth transition over time.
+ */
+public interface EaseSpecificEvent : Event {
+    /**
+     * The easing of the event.
+     */
+    public var ease: Easing
+}
+
+/**
+ * An [Event] that both has a duration and an easing.
+ */
+public interface DurationEaseSpecificEvent : DurationSpecificEvent, EaseSpecificEvent
+
 /**
  * An [Event] that is specific to a single row.
  */
diff --git a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetBackgroundColorEvent.kt b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetBackgroundColorEvent.kt
index 12bdf2e..d363b4f 100644
--- a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetBackgroundColorEvent.kt
+++ b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetBackgroundColorEvent.kt
@@ -25,7 +25,7 @@ public data class SetBackgroundColorEvent(
     @Flatten
     private var type: GroundType,
     var filter: RescaleFilter = RescaleFilter.NEAREST_NEIGHBOR,
-    override val rooms: RoomsOrTopLayer = roomsOf(ROOM1),
-) : ActionEvent(), RoomsOrTopLayerSpecificEvent {
+    override var rooms: RoomsOrTopLayer = roomsOf(ROOM1),
+) : ActionEvent(), MutableRoomsOrTopLayerSpecificEvent {
     public object Serializer : KSerializer<SetBackgroundColorEvent> by generatedSerializer().flatten()
 }
\ No newline at end of file
diff --git a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetForegroundEvent.kt b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetForegroundEvent.kt
index 870fe25..86df9c3 100644
--- a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetForegroundEvent.kt
+++ b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetForegroundEvent.kt
@@ -11,13 +11,17 @@ import cn.rdlevel.rdkt.core.serialization.Flatten
 import cn.rdlevel.rdkt.core.serialization.flatten
 import kotlinx.serialization.*
 
+/**
+ * Set foreground of rooms.
+ * @property type The type of the foreground.
+ */
 @Serializable(SetForegroundEvent.Serializer::class)
 @KeepGeneratedSerializer
 @SerialName("SetForeground")
 public data class SetForegroundEvent(
     @Flatten
     private var type: GroundType.Image,
-    override val rooms: RoomsOrTopLayer = roomsOf(ROOM1),
-) : ActionEvent(), RoomsOrTopLayerSpecificEvent {
+    override var rooms: RoomsOrTopLayer = roomsOf(ROOM1),
+) : ActionEvent(), MutableRoomsOrTopLayerSpecificEvent {
     public object Serializer : KSerializer<SetForegroundEvent> by generatedSerializer().flatten()
 }
diff --git a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetSpeedEvent.kt b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetSpeedEvent.kt
index 54d256e..4cb896f 100644
--- a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetSpeedEvent.kt
+++ b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetSpeedEvent.kt
@@ -5,6 +5,12 @@ import cn.rdlevel.rdkt.core.data.Easing
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
 
+/**
+ * Sets the speed of the level. Usually it will affect the speed of the event animations.
+ * @property speed The speed multiplier. 1.0 is the normal speed.
+ * @property duration The time to change to the target speed in beats.
+ * @property ease The easing function to use when changing the speed.
+ */
 @Serializable
 @SerialName("SetSpeed")
 public data class SetSpeedEvent(